Continual increases in the price of natural gas and fuel oil, and demands for generating electricity with reduced environmental impact, are stimulating advancements in technologies for deploying Integrated Gasification Combined Cycle (IGCC) power systems. Design of new power plants and retrofitting of older facilities, e.g., conversion of natural gas combined cycle (NGCC) plants to IGCC plants, present opportunities to develop systems and methods which increase overall power plant efficiencies.
In IGCC systems, a carbonaceous fuel such as coal is converted to a synthetic gas fuel, termed syngas. This is a mixture typically formed in a gasifier by partial oxidation of hydrocarbons at elevated temperatures. Oxygen-blown gasifiers typically source oxygen in order to minimize generation of by-products such as NOx compounds. An oxygen source can be developed in a high temperature air separation process which uses an Ion Transport Membrane (ITM) Air Separation Unit. When syngas is generated by gasification of coal with oxygen, typical constituents of the syngas include H2, CO, CO2, and CH4. Often the syngas will include impurities such as sulfides, nitrous components, and dust particles. The latter are normally removed from the mixture prior to combustion in order to provide an environmentally clean exhaust gas from the combustion turbine.
Syngas produced in an IGCC system is typically directed to a gas combustor for oxidation and generation of high pressure, high temperature exhaust which is sent to a gas turbine to provide a first source of mechanical power. Sensible heat, present in various fluids within the gasification subsystem of the IGCC system, or within the associated gas turbine subsystem, is commonly recovered by generating steam. Normally, most of the steam is routed through a turbine.
The efficiency of large scale commercial gasification systems are typically below 80 percent. Means of improving the efficiency of these and other power generating systems are desired, as even small improvements in plant efficiency have large impacts on the cost and viability of electrical power production from carbonaceous solid fuel sources.